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Strengthening Forensic Science in the United States: A Path Forward
parameters or quantities and ranges to be determined;
apparatus and equipment, including technical performance requirements;
reference standards and reference materials required;
environmental conditions required and any stabilization period needed;
description of the procedure, including
affixing of identification marks, handling, transporting, storing and preparation of items;
checks to be made before the work is started;
checks that the equipment is working properly and, where required, calibration and adjustment of the equipment before each use;
the method of recording the observations and results;
any safety measures to be observed;
criteria and/or requirements for approval/rejection;
data to be recorded and method of analysis and presentation;
the uncertainty or the procedure for estimating uncertainty.4
Uncertainty and Error
Scientific data and processes are subject to a variety of sources of error. For example, laboratory results and data from questionnaires are subject to measurement error, and interpretations of evidence by human observers are subject to potential biases. A key task for the scientific investigator designing and conducting a scientific study, as well as for the analyst applying a scientific method to conduct a particular analysis, is to identify as many sources of error as possible, to control or to eliminate as many as possible, and to estimate the magnitude of remaining errors so that the conclusions drawn from the study are valid. Numerical data reported in a scientific paper include not just a single value (point estimate) but also a range of plausible values (e.g., a confidence interval, or interval of uncertainty).
As with all other scientific investigations, laboratory analyses conducted by forensic scientists are subject to measurement error. Such error reflects the intrinsic strengths and limitations of the particular scientific technique. For example, methods for measuring the level of blood alcohol in an individual or methods for measuring the heroin content of a sample
Quoted from Section 5.4.4 of ISO/IEC 17025, “General requirements for the competence of testing and calibration laboratories” (2nd ed., May 15, 2005).